A Revision of the Genus Aulacodiseus Ehrb. By J. Rattray. 373 



near central space. Border striae 10 in • 01 mm., often punctate 1/24 

 to 1/28 of radius broad. Processes 3 to 7, insertion 1/4 to 1/6 of 

 radius from circumference, elongated, constriction wide, shallow, or 

 more sharp, free ends knob-like. Podiscus Rogersi Bail., Amer. 

 Journ. Sci., 1844, vol. xlvi. p. 137, pi. iii. figs. 1, 2. Podiscus 

 Rogersii var. senaria Bail., Ehrb. Mon. Ber. Ak., 1844, p. 81. 

 Podiscus Rogersii var. septenaria Bail., Ehrb., ibid., 1844, p. 81. 

 Eupodiscus Rogersii Ehrb., ibid., 1844, p. 81. Sch. Atl, pi. xcii. 

 figs. 2-6. Eupodiscus Bayleyi Ehrb., ibid., 1844 , p. 81. Aulaco- 

 diseus areolatus O'Me., Quart. Journ. Mic. Soc, 1878, p. 104. 



Podiscus was separated by Bailey from Tripodiseus Ehrb., as the 

 number of processes (" feet ") varied from 3 to 7. His P. Rogersi 

 var. senaria, with 6 processes, was accepted by Ehrenberg in 1844 as 

 the true Eupodiscus Rogersii Ehrb., his P. Rogersii var. septenaria, 

 with 7, then becoming Eupodiscus Baijleyi. O'Meara's association of 

 A. areolatus O'Me. with Coscinodiscus aster omphalus from Richmond, 

 Virginia, is erroneous. O'Meara regarded 6 as the prevailing number 

 of processes ; in the many specimens I have examined 3, 4, or 5 are 

 more common. 



Habitat : Petersburg, Va. (Ehrenberg) ; New Nottingham 

 deposit (Rae ! O'Meara !) ; Maryland (Oleve ! Witt, Griffin !). 



A. Argus Sch. Atl., pi. cvii. fig. 4.— Diam. 0-125 to • 19 mm. 

 Surface flat, sometimes slightly angular at processes, and convex 

 between these, the slope to border steep. Colour dark grey at centre, 

 almost opaque towards border. Central space absent. Markings 

 rounded, granular, in inconspicuous radial rows, most obvious in large 

 valves with wide meshes, mostly a few (3 or 4) at centre, and angles 

 of the smaller meshes, more numerous and along sides of larger; 

 recticulum coarse, meshes sometimes larger for 2/9 to 1/3 of radius 

 from centre,* their walls robust, often strongest at the angles, their 

 surface under reflected light rounded, with delicate finely undulating 

 closely placed lines, the meshes are arranged in radial rows, and 

 within border in several inconspicuous concentric bands. Border 

 indistinct, striae 8 to 10 in 0" 01 mm., 1/25 to 1/40 of radius broad. 

 Processes 3 to 5, insertion 1/3 to 1/5 of radius from circumference, 

 clavate, length 2.V times breadth, no clear space at base.— Tripodiseus 

 Argus Ehrb., Abh. Ber. Ak., 1839, p. 159, pi. iii. figs. Qa-c ; Tripo- 

 diseus germanicus Ehrb., ibid., 1839, Explan. pi. iii. figs. 6a-c; 

 Tetrapodiscus germanicus Ehrb., Mon. Ber. Ak., 1843, p. 166 ; 

 Pentapodiscus germanicus Ehrb., ibid., 1843; Eupodiscus ger- 

 manicus Ehrb., Mon. Ber. Ak., 1844, p. 81; Eupodiscus quater- 



* At ceiitre of valves meshes seen on surface sometimes unite at a slight depth 

 into larger meshes, of which the outlines are in focus at same time as interjacent 

 granules. Cuxhaven specimens belonging to "Weissflog, from which the upper layer 

 of valve has been removed, show the transparent lower layer with the processes still 

 attached. This layer has a rounded central space about 1/24 of diam. broad, the 

 markings are round granules, 4 in ■ 01 mm., with hyaline interspaces, and are arranged 

 in straight radial rows often disposed in pairs towards the centre, but more crowded 

 towards the border, which bears evident striae, and now appears sharply defined on 

 its inner side. 



